A broadband wireless access system based on IEEE802.16 system supports a power saving mode (or saving mode) for minimizing power consumption of a mobile station.
The operation of the mobile station in the power saving mode is performed by repetition of a sleep interval and a listening interval. The length of the sleep interval and the length of the listening interval, which are determined by each value of a sleep window and a listening window, have different values depending on characteristics of traffic set in a corresponding mobile station.
The sleep window and the listening window are parameters defined for the power saving mode. If the parameters including the sleep window and the listening window are defined and the power saving mode is activated depending on the defined parameters, the mobile station performs the power saving operation during the sleep interval defined by the value of the sleep window. In other words, the sleep interval represents the interval defined depending on the sleep window.
The listening interval is defined depending on the value of the listening window, and the mobile station can receive traffic during the listening interval.
Accordingly, the mobile station can have three types of power saving classes as follows depending on characteristics of traffic which is currently set.                Power Saving Mode Class of type 1        Power Saving Mode Class of type 2        Power Saving Mode Class of type 3        
The power saving mode class of type 1 targets a best effort (BE) having characteristics of an existing Internet traffic or a non-real-time variable rate (nrt-VR) in which a transmission rate is varied, and is defined by an initial sleep window, a final window base, a final window exponent, a listening window, and a start frame number for sleep window.
The power saving mode class of type 2 targets VoIP or a real-time variable rate (rt-VR) in which a transmission rate is varied, and is defined by an initial sleep window, a listening window, and a start frame number for sleep window.
The power saving mode class of type 3 is for either a management message, such as DCD/UCD and MOB_NBR-ADV, to be periodically forwarded to the mobile station which is in a power saving mode, or data to be forwarded in multicast, and is defined by a final window base, a final window exponent, and a start frame number for sleep window.
The following three messages are basically used for information exchange for the operation of each power saving mode class defined as above.
TABLE 1SyntaxSizeNotesMOB_SLP-REQ_Message_format( ) {—Management message type = 508 bits—Number of Classes8 bitsNumber of powersaving classes.for (i=0; i< Number of Classes; i++) {——Definition1 bit —Operation1 bit —Power_Saving_Class_ID6 bits—If (Operation = 1) | {——Start_frame_number6 bits—Reserved2 bits—}——If (Definition = 1) {——Power_Saving_Class_Type2 bits—Direction2 bits—Traffic_triggered_wakening_flag1 bit —Reserved3 bits—initial-sleep window8 bits—listening-window8 bits—Final-sleep window base10 bits —Final-sleep window exponent3 bits—Number_of_CIDs3 bits—for (i=0; i<Number_of_CIDs; i++ {——CID16 bits —}——}——TLV encoded informationvariable———
Table 1 illustrates an example of MAC management message which is forwarded from the mobile station to a service base station to request a sleep mode which includes a sleep interval and a listening interval.
TABLE 2SyntaxSizeNotesMOB_SLP-RSP_Message_format( ) {——Management message type = 518 bits—Number of Classes8 bitsNumber of power savingclasses.for (i = 0; i < Number_of_Classes; i++) {——Length of Data7 bits—Sleep Approved1 bit Definition1 bit —Operation1 bit —Power_Saving_Class_ID6 bits—if (Sleep Approved == 1) {——if (Operation = 1) {——Start_frame_number6 bits—Reserved2 bits—}——if (Definition = 1) {——Power_Saving_Class_Type2 bits—Direction2 bits—Initial-sleep window8 bits—listening window8 bits—final-sleep window base10 bits —final-sleep window exponent3 bits—TRF-IND required1 bit —Traffic_triggered_wakening_flag1 bit —Reserved1 bit —if (TRF-IND required) {——SLPID10 bits —Reserved2 bits—}——Number_of_CIDs4 bits—for (i = 0; i < Number_of_CIDs; i++) {——CID16 bits —}——if (MDHO or FBSS capability enabled) {—If MDHO or FBSS capability isenabled in the REG-REQ/RSPmessage exchange.Maintain Diversity Set and Anchor BS1 bit —if (Maintain Diversity Set and Anchor BS) {——MDHO/FBSS duration (s)3 bits—}——}——}——PaddingvariableIf needed for alignment to byteboundary} else {—In case Sleep Approved == 0REQ-duration8 bits}TLV encoded informationvariable—}——
Table 2 illustrates an example of MAC management message which is forwarded from the service base station to the mobile station to forward sleep mode related information as to whether to accept the sleep mode through sleep response, the sleep interval, the listening interval, and sleep ID.
TABLE 3SyntaxSizeNotesMOB_TRF-IND_Message_format( )——{Management message type = 528 bits—FMT1 bit —if (FMT == 0) {——SLPID Group Indication bit-map32 bits N-th bit of SLPID-Group indication bit-map MSBcorresponds to N = 0] is allo-cated to SLPID Groupthat includes MS with SLPID values from N*32 toN*32 + 31Meaning of this bit 0: There is no traffic for all the32 MS that belong to the SLPID-Group 1: There istraffic for at least one MS in SLPID-Group.Traffic Indication BitmapvariableTraffic Indication bit map comprises the multiples of32-bit long Traffic Indication unit. A TrafficIndication unit for 32 SLPIDs is added toMOB_TRF-IND message whenever its SLPIDGroup is set to 1 32 bits of Traffic Indication Unit(starting from MSB) are allocated to MS in theascending order of their SLPID values: 0: Negativeindication 1: Positive indication} else {——Num_Pos8 bitsNumber of CIDs followingfor (i=0; i<Num_Pos; i++) {——SLPIDs10 bits —}——}——PaddingvariableIf needed, for aligmnent to byte boundary.TLV encoded itemsvariable—}——
Table 3 illustrates an example of a broadcast type traffic notification message forwarded at a constant interval. The mobile station of the sleep mode receives the traffic notification message during the listening interval so that it is notified the presence of a downlink traffic forwarded thereto. Then, the mobile station of the sleep mode determines whether to continue to maintain the sleep mode or to receive downlink data after ending the sleep mode.
The operation of each class will be described in detail through the following description of the operation of a technical device according to the related art.
1. Operation of Power Saving Mode Class of Type 1
FIG. 1 is a flow chart illustrating the operation procedure of the power saving mode class of type 1.
In the power saving mode class of type 1, the mobile station requests the base station of conversion to the power saving mode, maintains the power saving mode, and then ends the power saving mode as downlink traffic occurs in the corresponding mobile station.
The operation shown in FIG. 1 will be described as follows.
The mobile station sets values such as initial sleep window, final sleep window, and listening window in a sleep request message (message of Table 1) and forwards the set values to the base station to request conversion to the power saving mode (S101).
If the base station allows conversion to the power saving mode of the corresponding mobile station, the base station forwards a sleep response message (message of Table 2) to the mobile station (S102), wherein values such as initial sleep window, final sleep window, listening window, and initial frame number of sleep window are set in the sleep response message.
If the conversion time to the power saving mode starts, the mobile station maintains a sleep interval equivalent to that of the initial sleep window (S103). In other words, the sleep interval corresponds to the value of the initial sleep window.
If the sleep interval expires, the mobile station receives the traffic notification message (message of Table 3) from the base station for the listening interval preceded by the sleep interval. In case of no downlink traffic toward the mobile station (negative indication), the mobile station maintains the power saving mode for a time period equivalent to twice of the initial sleep window (S104). In other words, the sleep interval corresponds to twice of the value of the initial sleep window.
The sleep interval continues to increase through the following equation (set next sleep window to twice of previous sleep window). The size of the final sleep window is set as follows through final window base and final window exponent which are determined through the sleep response message (message of Table 2) (S105).final sleep window=final sleep window base*2 final window exponent   [Equation 1]
If the mobile station receives the traffic notification message for the listening interval (positive indication), the mobile station ends the power saving mode (S106), wherein the traffic notification message indicates downlink traffic toward the mobile station.
2. Operation of Power Saving Mode Class of Type 2
Hereinafter, the power saving mode class of type 2 will be described.
FIG. 2 is a flow chart illustrating the operation procedure of the power saving mode class of type 2 of a mobile station which is using an unsolicited grant service (UGS) and a real time variable service (RT-VR), wherein the UGS provides one fixed data rate and the real time variable service (RT-VR) provides one real-time variable data rate.
The operation procedure will be described as follows.
The mobile station forwards the sleep request message illustrated in Table 1 to the base station to request definition of power saving mode class parameters (S201).
The base station which has received the sleep request message sets a fixed sleep interval and a fixed listening interval in the sleep response message so as to allow the mobile station to define the power saving mode class parameters (S202).
The mobile station forwards the sleep request message illustrated in Table 1 to the base station to request activation of the power saving mode (S203).
The base station which has received the sleep request message sets a start frame representing a conversion time to the power saving mode in the sleep response message illustrated in Table 2 so as to grant activation of the power saving mode (S204).
The mobile station maintains the power saving mode for a time period equivalent to the sleep interval at the conversion time to the power saving mode (S205).
If the sleep interval expires, the mobile station synchronizes with the base station to maintain uplink/downlink communication with the base station, and receives downlink data from the base station and transmits uplink data to the base station for the listening interval (S206).
If the listening interval expires, the mobile station maintains the power saving mode for the sleep interval to save the power. Afterwards, the mobile station is operated in the power saving mode by repeating the step S204 and the step S205 (S207).
If the mobile station desires to deactivate the power saving mode class, the mobile station forwards a sleep request message representing deactivation of the power saving mode to the base station (S208).
The base station which has received the sleep request message forwards the sleep response message to the mobile station to grant deactivation of the power saving mode (S209).
After inactivating the power saving mode class, the mobile station is normally operated (S210).
3. Operation of Power Saving Mode Class of Type 3
Hereinafter, the power saving mode class of type 3 of the mobile station which is maintained in multicast connection will be described.
FIG. 3 illustrates the power saving mode class of type 3 for reducing power consumption in the mobile station which receives data from the base station through multicast connection.
The base station forwards the sleep response message to the mobile station to allow the mobile station to perform conversion to the power saving mode class of type 3 (S301).
If the conversion time (start frame) to the power saving mode starts, the mobile station which has received the sleep response message maintains the power saving mode for the sleep interval (S302). The sleep interval is determined by the sleep window.
If the sleep interval expires, the mobile station maintains the state capable of performing communication with the base station, and receives data forwarded from the base station through multicast connection (S303).
If the base station forwards all data in a state that multicast connection is maintained, the base station forwards the sleep response message to allow the mobile station to perform conversion to the power saving mode class of type 3, so that the mobile station saves the power until next multicast data are transmitted (S304).
If the conversion time to the power saving mode starts, the mobile station which has received the sleep response message maintains the power saving mode for the sleep interval (S305).
The steps (S303), (S304), and (S305) are repeated (S306).
As described above, the broadband wireless access system supports the power saving mode class per connection according to service type, so as to reduce power consumption of the mobile station.
FIG. 4 illustrates the operation of the power saving mode of the mobile station in which several power saving classes are activated.
In FIG. 4, intervals of unavailability are formed in a region where the sleep intervals are overlapped, and intervals of availability are formed in the other intervals.
In case that a plurality of power saving schemes are used, intervals where sleep intervals according to the respective power saving schemes are overlapped correspond to intervals of unavailability. Also, the other intervals excluding the intervals of unavailability correspond to intervals of availability.
As shown, the mobile station in which several power saving classes are activated temporarily disables uplink/downlink communication with the base station to avoid power consumption for the interval where sleep intervals per class are overlapped.
The power saving mode is operated by the following two steps.                definition of power saving class: there is provided the first step of defining power saving parameters such as sleep window, listening window, sleep ID, and connection identifier. A unique power saving class identifier is assigned depending on the defined power saving class. If there are provided different power saving parameters for one power saving class, different power saving class identifiers are assigned.        There is provided the second step of performing the operation of the power saving class. The operation of the defined power saving class is activated or the operation of the activated power saving class is deactivated.        
FIG. 5 illustrates the operation of the mobile station which is in the power saving mode.
To define the power saving class, the mobile station in the normal operation mode forwards the sleep request message to the service base station, wherein the sleep request message includes power saving parameters such as power saving class type, connection direction, initial sleep window, listening window, final sleep window, final sleep window exponent, traffic indicator flag, and connection ID. At this time, a definition field is set to 1 to indicate the sleep request message for defining the power saving class (S501).
The base station which has received the sleep request message forwards the sleep response message to the mobile station (S502), wherein the sleep response message includes power saving parameters such as power saving class type, connection direction, initial sleep window, listening window, final sleep window, final sleep window exponent, traffic indicator flag, sleep ID, and connection ID.
To request conversion to the power saving mode, the mobile station should forward the sleep request message to the base station (S503), wherein the sleep request message includes the operation field set to 1. At this time, the mobile station transmits the sleep request message along with a start time of the power saving mode.
The base station which has received the sleep request message of which operation field is set to 1 forwards the sleep response message to the mobile station, wherein the sleep response message includes the operation field set to 1 and the conversion start time to the power saving mode (S504).
The mobile station which has received the sleep response message is converted into the power saving mode at the start time (S505).
The mobile station does not receive a downlink signal forwarded from the service base station for the sleep interval, which is the unavailable communication time period, to minimize power consumption, and does not transmit uplink traffic to the service base station (S506).
The mobile station can receive downlink data from the service base station and transmit uplink data to the service base station for the listening interval which is the available communication time period (S507).
If the listening interval expires, the mobile station maintains the power saving mode for a time period equivalent to the sleep interval to avoid power consumption (S508).
The mobile station performs transmission and reception of uplink/downlink data with the service base station for the listening interval (S509).
If the mobile station should deactivate the power saving class during the listening interval, the mobile station transmits the sleep request message or a sleep control header to the base station to indicate deactivation of the power saving mode, wherein the sleep request message includes the operation field set to 0 (S510).
The service base station which has received the deactivation request of the power saving mode through the sleep request message or the sleep control header forwards the sleep response message to the mobile station to indicate deactivation of the corresponding power saving class, wherein the sleep response message includes the operation field set to 0 (S511).
The mobile station which has received the sleep response message of which operation field is set to 0 deactivates the corresponding power saving class to end the power saving mode. However, if a plurality of power saving classes are activated, the operation of the corresponding power saving class can only be deactivated (S512).
Although the definition and the operation of the power saving class according to the related art have been described based on the two steps, the mobile station and the base station may define the power saving class and at the same time perform activation of the corresponding power saving class by exchanging the sleep request message and the sleep response message, of which definition field and operation field are simultaneously set to 1.
Furthermore, according to the related art, the base station can activate/deactivate the power saving mode by forwarding the sleep response message or downlink sleep control header message to the mobile station without request of the mobile station.